1. Field of the Invention
The present invention relates to a structure of a breather device for an engine, made in a valve arm chamber that covers an upper side of a cylinder head.
2. Background Art
Conventionally, an engine has a breather chamber in a valve arm casing that covers an upper side of a cylinder head of an engine is formed a breather chamber, in which blow-by gas including oil mist is separated into oil component and gas component.
This breather chamber is made as a space surrounded by side walls of the valve arm casing, ribs jutting from inside surfaces of the valve arm casing, and a base plate installed at regular intervals from the inside surfaces of the valve arm casing. A filter gauze arranged in the breather chamber traps oil mist (oil component) in blow-by gas, and removes it from the gas.
However, the conventional breather device merely comprising the filter gauze at an inlet portion of the breather chamber has insufficient ability for removing oil component. Moreover, if a structure of recirculating the blow-by gas having passed the breather chamber into intake gas is applied, the intake gas is mixed with oil, thereby increasing emission in exhaust gas far from decreasing it.
A pressure-regulating valve is arranged at an outlet portion of the breather chamber for blow-by gas so as to regulate pressure in the breather chamber. As shown in FIG. 14, for instance, a conventional pressure-regulating valve 40 comprises a diaphragm 41, a spring 42, and a center plate 43, so that the spring 42 energizes the diaphragm 41 downward, with the center plate 43 put between the spring 42 and the diaphragm 41. The diaphragm 41 cuts off communication between a gas passage 44 to the intake side and a breather chamber 45. When the pressure in the breather chamber 45 arises above a predetermined pressure, the diaphragm 41 is pressed and moved upward, so that the pressure-regulating valve 40 opens to bring the breather chamber 45 into communication with the gas passage 44.
This conventional pressure-regulating valve requires such many parts of the spring 42 and the center plate 43, thereby being expensive and complicated.
A conventional breather chamber is connected to an intake manifold through a breather pipe for recirculating blow-by gas through the breather chamber into intake gas. However, if the negative pressure in intake side is propagated into the valve arm chamber at a breath, blow-by gas is let into the intake manifold rapidly, so that much oil component moves to the intake side at a breath, therefore engine performance falls down.